TGDMLParse

creates the new instance of the XMLEngine called 'gdml', using the filename 
then parses the file and creates the DOM tree. Then passes the DOM to the 
next funtion to translate it. 

this function recursively moves thru the DOM tree of the GDML file. It checks for
key words along the way and if a key word is found it calls the corresponding
function to interpret the node.

takes in a string containing a mathematical expression and
returns the result of the expression as a double.

When using the 'divide' process in the geometry this function
sets the variable 'axis' depending on what is specified.

this function looks thru a string for the chars '0x' next to
each other, when it finds this, it calls another function to strip
the hex address.   It does this recursively until the end of the 
string is reached, returning a string without any hex addresses.

this function is passed a string, and removes the first hex address
it finds.   This function is called recursively by NameShort to
fully strip a string of all hex addresses within it.

If a value is given within the GDML file, this function checks
the constant map set up when all constants are declared.   If a matching
constant name is found, the corresponding value is returned, if not,
the original is returned.

In the define section of the GDML file, constants can be declared.
when the constant keyword is found, this function is called, and the
name and value of the constant is stored in fconmap map using the 
constant name as its key.

Throughout the GDML file, a unit can de specified.   Whether it be
angular or linear, values can be used as well as abbreviations such as
 'mm' or 'deg'. This function is passed the specified unit and if it is 
found, replaces it with the appropriate value.

In the define section of the GDML file, positions can be declared.
when the position keyword is found, this function is called, and the
name and values of the position are converted into type TGeoPosition 
and stored in fposmap map using the name as its key. This function 
can also be called when declaring solids.

In the define section of the GDML file, rotations can be declared.
when the rotation keyword is found, this function is called, and the
name and values of the rotation are converted into type TGeoRotation 
and stored in frotmap map using the name as its key. This function 
can also be called when declaring solids.

In the materials section of the GDML file, elements can be declared.
when the element keyword is found, this function is called, and the
name and values of the element are converted into type TGeoElement and
stored in felemap map using the name as its key.

In the materials section of the GDML file, materials can be declared.
when the material keyword is found, this function is called, and the
name and values of the material are converted into type TGeoMaterial 
and stored in fmatmap map using the name as its key. Mixtures can also
 be declared, and they are converted to TGeoMixture and stored in
fmixmap.   These mixtures and materials are then all converted into one
common type - TGeoMedium.   The map fmedmap is then built up of all the 
mixtures and materials.

In the structure section of the GDML file, volumes can be declared.
when the volume keyword is found, this function is called, and the
name and values of the volume are converted into type TGeoVolume and
stored in fvolmap map using the name as its key. Volumes reference to 
a solid declared higher up in the solids section of the GDML file. 
Some volumes reference to other physical volumes to contain inside 
that volume, declaring positions and rotations within that volume. 
When each 'physvol' is declared, a matrix for its rotation and 
translation is built and the 'physvol node' is added to the original 
volume using TGeoVolume->AddNode.
volume division is also declared within the volume node, and once the
values for the division have been collected, using TGeoVolume->divide,
the division can be applied.

In the solid section of the GDML file, boolean solids can be 
declared. when the subtraction, intersection or union   keyword 
is found, this function is called, and the values (rotation and 
translation) of the solid are converted into type TGeoCompositeShape
and stored in fsolmap map using the name as its key.

1 = SUBTRACTION
2 = INTERSECTION
3 = UNION

In the structure section of the GDML file, assembly volumes can be 
declared. when the assembly keyword is found, this function is called, 
and the name is converted into type TGeoVolumeAssembly and
stored in fvolmap map using the name as its key. Some assembly volumes 
reference to other physical volumes to contain inside that assembly, 
declaring positions and rotations within that volume. When each 'physvol' 
is declared, a matrix for its rotation and translation is built and the 
'physvol node' is added to the original assembly using TGeoVolume->AddNode.

In the setup section of the GDML file, the top volume need to be 
declared. when the setup keyword is found, this function is called, 
and the top volume ref is taken and 'world' is set

In the solids section of the GDML file, a box may be declared. 
when the box keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoBBox and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Paraboloid may be declared. 
when the paraboloid keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoParaboloid and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, an Arb8 may be declared. 
when the arb8 keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoArb8 and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Tube may be declared. 
when the tube keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoTubeSeg and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Cut Tube may be declared. 
when the cutTube keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoCtub and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a cone may be declared. 
when the cone keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoConSeg and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Trap may be declared. 
when the trap keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoTrap and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Trd may be declared. 
when the trd keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoTrd2 and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Polycone may be declared. 
when the polycone keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoPCon and stored in fsolmap map using the name 
as its key. Polycone has Zplanes, planes along the z axis specifying 
the rmin, rmax dimenstions at that point along z.

In the solids section of the GDML file, a Polyhedra may be declared. 
when the polyhedra keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoPgon and stored in fsolmap map using the name 
as its key. Polycone has Zplanes, planes along the z axis specifying 
the rmin, rmax dimenstions at that point along z.

In the solids section of the GDML file, a Sphere may be declared. 
when the sphere keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoSphere and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Torus may be declared. 
when the torus keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoTorus and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Hype may be declared. 
when the hype keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoHype and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a Para may be declared. 
when the para keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoPara and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a TwistTrap may be declared. 
when the twistedtrap keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoGTra and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, a ElTube may be declared. 
when the eltube keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoEltu and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, an Orb may be declared. 
when the orb keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoSphere and stored in fsolmap map using the name 
as its key.

In the solids section of the GDML file, an Xtru may be declared. 
when the xtru keyword is found, this function is called, and the 
dimensions required are taken and stored, these are then bound and
converted to type TGeoXtru and stored in fsolmap map using the name 
as its key. The xtru has child nodes of either 'twoDimVertex'or 
'section'.   These two nodes define the real structure of the shape.
The twoDimVertex's define the x,y sizes of a vertice. The section links
the vertice to a position within the xtru. 

In the solids section of the GDML file, a Reflected Solid may be 
declared when the ReflectedSolid keyword is found, this function 
is called. The rotation, position and scale for the reflection are 
applied to a matrix that is then stored in the class object 
TGDMLRefl.   This is then stored in the map freflsolidmap, with 
the reflection name as a reference. also the name of the solid to 
be reflected is stored in a map called freflectmap with the reflection 
name as a reference.